The present invention relates to a grooving apparatus for cutting a tread pattern in tires.
Conventionally, a hand cutter was generally used for manually grooving tires which were produced for testing purposes or on a small scale production basis, i.e., for forming a tread groove pattern in vulcanized plain tires having no tread pattern. This manual procedure requires skill and is time-consuming. For large size tires having a relatively simple groove pattern, therefore, Unexamined Japanese Patent Publication No. SHO 56-162633, for example, discloses an apparatus which comprises a shaft for supporting a tire, a support frame movable axially with respect to the shaft and perpendicular to the shaft, and a cutter shaft mounted on the support frame, directed toward the surface of the tire to be worked on and rotatable according to the angle of the groove to be formed, such that a cutter is heated and caused to cut into a shoulder face of the tire. For heating and movement along the contemplated pattern, the cutter is controlled by a programmed computer.
Although large size tires generally have simple tread patterns which can be formed by relatively simple movement of the heated cutter, small size tires such as passenger car tires have grooves of complex shapes which require complex movement of the cutter. The prior art devices are not always capable of meeting this requirement. Further, because the pattern grooves are cut by the heated cutter and the rubber portion around the cutter is heated, for example, to a temperature of about 200.degree. C. or higher, it is very likely that the physical properties of the vulcanized rubber change the elasticity of the rubber is impaired and the quality of the tire is adversely affected. The heating is also likely to scorch or melt the neighboring rubber portion, failing to form grooves of a clear-cut shape or to assure the required running characteristics fully. When forming grooves of a double stepped shape, the cutter will burn out so as to become inoperative. Another problem encountered is that the heating reduces the durability of the cutter.
Although it appears possible to use a multi-articulated robot for supporting the cutter for grooving, the cutter shaft must then be given greater freedom, which renders the control program complex, thus making the tire grooving apparatus expensive.